This invention relates generally to gas turbine engines, and, more particularly, to gas turbine engine combustors. One form of the present invention is directed to a combustor dome module.
Gas turbine engines with high specific thrust (that is, high thrust of the engine per engine area) require combustion liners capable of burning more fuel per volume compared to conventional combustors. Combustion in a gas turbine is generally accomplished via three stages: 1) fuel injection, 2) fuel mixture with air (oxidant), and finally 3) fuel/air mixture multi-step chemical reaction to obtain the gas temperature rise necessary to drive the engine and its payload. For a given design space in a combustion liner, only so much fuel can be burned efficiently without delivering unburned products. Mixing limitations arise due to the fact that all three of the above processes require a finite amount of time. If one is to enhance the limitations of a conventional combustor by adding more fuel to burn, some of these stages must be performed more efficiently within the allotted time and space. It is generally understood that the volume and size of the combustor is established by the cumulative residence time of all processes that take place in the combustion chamber.
Conventional annular combustion liners inject fuel at discrete circumferential locations inside the reaction zone, thereby creating circumferential fuel/air ratio non-uniformities that translate into temperature non-uniformities at the combustion liner exit. These combustor exit temperature non-uniformities eventually create turbine aerodynamic and material durability performance degradation.
The need, therefore, exists for a gas turbine combustor that allows the three stages of combustion to be performed more efficiently. The present invention meets this need in a novel and non-obvious way.
The present invention performs the fuel injection and mixing, two of the three necessary stages for combustion, outside of the reaction zone in a pre-mixing zone. One form of the present invention contemplates a combustor module that includes an annular pre-vaporizing chamber defined by an inner wall, and an outer wall, and a heat shield. The heat shield separates the pre-mixing zone from the reaction zone of the combustor. Fuel is injected into the pre-vaporizing chamber and sprayed onto the surface of the heat shield, thereby simultaneously vaporizing the fuel and cooling the heat shield. The heat shield also includes a pilot fueling spray opening to allow fuel to pass directly into the reaction zone to provide a piloting flame stability region therein.
In one embodiment of the combustor module of the present invention, the premixed fuel and air enter the reaction zone in an annularly uniform mannerxe2x80x94a desirable result when such a module is coupled to an annular combustion liner configuration. This unique combustor module reduces the circumferential non-uniformities since the fuel and air are pre-mixed prior to entering the reaction zone. Further, the combustor module of the present invention permits optimization of the pre-mixing zone for the first two combustion stages so that the reaction zone can be optimized for the last combustion stage. Effective fuel/air premix is accomplished by delivering fuel using a multi-hole fueling spray nozzle capable of directing the fuel to the location needed for best fuel evaporation and best mixing within the pre-mixing zone. Fuel and air mixture inside this mixing region will be well in excess of the flammability limits of the fuel to prevent reaction from occurring prior to admitting the mixture into the reaction zone.
The dome features of the combustor according to one form of the present invention are designed to divert the fuel/air mixture exiting the pre-mixing zone in the following manner. First, some of the mixture is diverted towards the concave region formed by the heat shield to create a reacting trapped vortex at the center portion of the reaction zone. This reacting trapped vortex provides the anchoring flame necessary to maintain combustion stability within the reaction zone. This anchoring flame is located very close to the heat shield; consequently, the survivability of the heat shield depends on the backside cooling effectiveness of the fuel impingement/vaporization in the pre-mixing zone. Secondly, the remainder of the fuel/air mixture is diverted and further diluted with air entering the reaction zone through inner and outer swirlers. The combustion reaction, thus, occurs immediately downstream of the dome. The present invention promotes the combustion reaction nearest the dome to allow additional residence time to mix out any non-uniformities in the gas flow before the flow enters the turbine hardware.
The combustor module according to the present design, therefore, promotes rapid combustion inside the reaction zone of the combustor since residence time required for fuel injection and mixing has been already performed in the mixing region. Shortening the combustion residence time has a direct effect in shortening the combustor volume, or alternatively, it can increase the temperature rise of the combustor for a given combustor volume. A combustor equipped with such a combustor module is also capable of delivering a more uniform exit temperature pattern that benefits turbine performance and durability.
One object of the present invention is to provide a unique combustor module for a gas turbine engine.
Related objects and advantages of the present invention will be apparent from the following description.